Reversibly wireable evaporator coil freeze-over prevention device

ABSTRACT

Heating, Ventilating, and Air Conditioning (HVAC) and refrigeration systems have a thermostat to allow users to set a desired temperature for living and storage spaces. The output from the thermostat is a so-called “Call for Cool” signal (CfC) used to start the system compressor and begin the cooling process. A circuit which interrupts the CfC signal from a thermostat to the compressor without using specific input and output connections to define the CfC signal is disclosed. The circuitry monitors the temperature of the evaporator, and if the temperature dips too low, the compressor is disengaged until the measured temperature rises above a safe level.

FIELD OF THE INVENTION

The present invention relates to refrigeration and Heating, Ventilating and Air Conditioning (“HVAC”) control systems, and more particularly pertains to a simple to install device that prevents evaporator freeze-over and subsequent compressor failure. Hereinafter referred to as “NoIce.”

BACKGROUND OF THE INVENTION

A refrigeration system and the air conditioning part of a Heating, Ventilating, and Air Conditioning (“HVAC”) system serve two purposes: they both cool and de-humidify the air circulated through them. These functions have been well described in the prior art, U.S. Pat. No. 2,932,178, Armstrong, et. al. and the typical refrigerant loop is shown in FIG. 1.

Several problems develop if the refrigerant level in the system drops below ideal, or the conditioned space is very humid. The low temperature derived from the vaporizing refrigerant creates a cold zone in the evaporator immediately past the metering device. Moisture deposited in this area freezes and blocks air flow through the frozen portion of the evaporator. Ice is a good insulator, so over time the cold zone extends further into the evaporator, which expands the frozen area. As detailed in U.S. Pat. No. 3,845,637, Shepherd, once a sufficient amount of the evaporator is coated in ice, the refrigerant no longer vaporizes and liquid refrigerant returning to the refrigerant compressor causes the compressor to fail.

System configurations to prevent compressor failure due to evaporator freeze-over are known in the prior art U.S. Pat. No. 2,688,850, White. These configurations are necessarily built into the refrigeration and HVAC systems at the time of manufacture and cannot be retrofit into existing installations. While these system configurations may have met their particular objectives and requirements, the prior art does not describe a reversibly wireable evaporator freeze-over prevention device that is simple to install.

In HVAC and refrigeration systems, standalone timer relays are integrated into the refrigerant compressor control line (the so-called “call for cool” (“CfC”) command line) to keep the compressor from restarting for a pre-set time if power is interrupted while the compressor is running. In the industry, these relays are called “pressure release timers”, and this time delay function is essential to keep a compressor from failing due to disturbances on the power line (thunderstorms, etc.) The schematic of the system with a pressure release timer is shown in FIG. 2.

If evaporator ice buildup is a problem, the device most often used in the industry today to prevent ice buildup is a separate timer relay that periodically puts the system into a “defrost mode” to allow any ice that may have formed in the evaporator to melt, as described in U.S. Pat. No. 5,870,899, Byung-Joon Choi. This defrost timer is installed in the CfC line in series with the pressure release timer, and is typically attached when the system is first installed. It is meant to be installed by skilled workers because it is powered from the main system power and runs continuously. This relay may solve an ice buildup problem, but it offers the owner no warning that an ice buildup problem exists, and it is inefficient because the “defrost mode” is invoked whether there is ice present or not. The defrost timer added to the typical control system is shown in FIG. 3.

As described earlier, an HVAC or refrigeration system uses a control wire to connect the thermostat to the compressor. The reversibly wireable evaporator freeze-over prevention device described herein, which is also referred to as the NoIce Control, may replace both the defrost timer and the pressure release timer, see FIG. 4.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth will become apparent when consideration is given to the following descriptions. Such descriptions refer to these drawings wherein:

FIG. 1 is a pictorial diagram of a typical air conditioning system refrigerant loop.

FIG. 2 is the schematic diagram of a typical compressor control system.

FIG. 3 is the schematic diagram of a compressor control system with a defrost timer installed to control ice buildup.

FIG. 4 is the schematic of a compressor control system with the NoIce Control installed.

FIG. 5 is a block diagram showing the major components of the NoIce circuit.

FIG. 6 is a wiring schematic diagram of the herein described preferred embodiment of the NoIce circuit.

FIG. 7(a)-7(b) is a representation (flow chart) of the program that operates the NoIce Control.

DETAILED DESCRIPTION OF THE INVENTION

The color of the CfC wire is standardized throughout the HVAC and refrigeration industry, and is well known to installers. The present invention is installed in the control circuit between the thermostat and the compressor just as defrost timers are, using wires matching the color-code of the CfC control wire. The term “reversibly wireable” means that like color-coded wires may be connected in either of two possible configurations: one of the like color-coded wires is connected to the compressor and the other like color-coded wire is connected to the thermostat, or vice-versa; the wires are interchangeable. The device is designed to be installed by technicians either during or after the initial system installation, and is thus simple to install, a key objective. The NoIce Control requires power only when the CfC command is active, so eliminates the need for connection to the main power portion of the HVAC or refrigeration system, attaining another key objective. It is energy efficient because it monitors the temperature of the evaporator only when it is powered, and acts only when ice is detected. The NoIce Control may also alert the user if the evaporator has frozen over, achieving yet another key objective. The program in the NoIce Control, which is a part of the device, is shown in flowchart form in FIGS. 7(a) and 7(b).

In this respect, the reversibly wireable evaporator freeze-over prevention device, according to the present invention, substantially departs from the concepts and designs of the prior art. The general purpose of the present invention is to provide a new and improved evaporator freeze-over prevention device, which has all the advantages of the prior art and none of the disadvantages. It provides a device exclusively developed to prevent air conditioner and refrigeration evaporator freeze-over that is simple to install, is energy efficient, uses only CfC and common connections, and alerts the user to incipient compressor failure.

In describing this invention, the word “coupled” means that the article or structure referred to is joined, either directly or indirectly, to another article or structure. The term “electronically coupled” means that the devices which are electronically coupled form part of the described circuit. By way of example, an engine starter is electronically coupled to a car battery. Also, when used as a noun to describe a component, the words “connection” and “connector” are interchangeable, that being a physical element to which another item is coupled or attached.

Referring to FIG. 4, there are three wires connected to the NoIce Control: two like color-coded wires for connection to the thermostat and compressor, and a third wire connected to the system transformer, known in industry parlance as “thermostat common”. Now referring to FIG. 5, the two like color-coded wires are items 12 and 14. These plus the thermostat common wire (item 16) are all routed to block 10, the “RECTIFIER/REGULATOR”, where they are rectified and regulated to provide the electrical power necessary to operate the rest of the circuitry.

There is a controller provided to measure the necessary temperatures, provide timing functions for the pressure release and defrost mode, provide signals to alert the user to ice buildup, and to control the driver. This device is identified as block 20, “CONTROL” in FIG. 5.

The temperature sensor interface has a connection to the controller, and connections for the temperature sensor. This is identified as block 30, “INTERFACE” in FIG. 5.

There is a driver provided to operate the interrupter in the CfC line. This device is identified as block 40, the “DRIVER” in FIG. 5.

The temperature sensor itself is identified as block 50, “TEMPERATURE SENSOR” in FIG. 5.

There is an electrical interrupter provided to disconnect the signal between the thermostat CfC line and the compressor. This device is identified as block 60, the “INTERRUPTER” in FIG. 5.

Thus there has been outlined broadly some of the more important features of the invention in order that the detailed description thereof that follows may be better understood and that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached.

The invention is not limited in its application to the details of construction or arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of descriptions and should not be regarded as limiting.

It is therefore an object of the present invention to provide a new and improved reversibly wireable evaporator freeze-over prevention device for the refrigeration and HVAC industries that has all of the advantages, and none of The disadvantages, of the prior art systems to prevent evaporator freeze-over and subsequent compressor failure.

It is another object of the present invention to provide a new and improved a reversibly wireable evaporator freeze-over prevention device for the refrigeration and HVAC industries that may be easily and efficiently manufactured and marketed.

It is a further object of the present invention to provide a new and improved reversibly wireable evaporator freeze-over prevention device for the refrigeration and HVAC industries that is of durable and reliable constructions.

Still another object of the present invention is to provide a new and improved reversibly wireable evaporator freeze-over prevention device for the refrigeration and HVAC industries that is simple to install.

Lastly, it is an object of the present invention to provide a new and improved reversibly wireable evaporator freeze-over prevention device for the refrigeration and HVAC industries that operates in an energy efficient manner.

Detailed Description of the Preferred Embodiment

The present invention, a reversibly wireable evaporator freeze-over prevention device, or NoIce Control, is shown in block form in FIG. 5. Such components in their broadest context include an alternating current to direct current converter and regulator (block 10), a controller (block 20), a sensor interface (block 30), a driver (block 40), a temperature sensor (block 50), an interrupter (block 60), and an alert device (block 70). Such blocks are individually configured and connected to each other so as to attain the desired objectives.

Connected to the NoIce Control in FIG. 5 is a pair of like color coded wires, being a first like color coded wire 12 and a second like color coded wire 14. The wires are color coded using industry standard coloration, so that an installer can apply the device with one of the wires being electronically coupled to a compressor and the other like color coded wire being electronically coupled to a thermostat. The NoIce control is unique in that it does not matter which of the like color coded wires is connected to the compressor or the thermostat, proper circuit operation will still result. There is a third wire 16 electronically connected to the NoIce Control called “thermostat common”. These wires provide power to the NoIce Control.

The electronic components comprising each of the blocks from FIG. 5 are identified in FIG. 6. Several design optimizations are implemented to minimize the costs of building this design.

The RECTIFIER/REGULATOR (FIG. 5, block 10) is comprised of electronic components D2, F1, C1, R8-R10, D4, C3-C5, and U2 in FIG. 6. D2, F1, and C1 form a classical half-wave rectified AC-to-DC power converter. The DC voltage produced is higher than the operating voltage of the controller (U1), so several, low-tolerance resistors (R8-R10, Yageo RC1206FR-07274RL), a Zener diode (D4, Fairchild BZX84C12), low-cost capacitors (C3-C5), and an inexpensive voltage regulator (U2, TI LM78L05ACM) combine to lower and regulate the voltage produced to that needed by U1. None of these component values are critical to proper circuit operation, and other parts may be substituted without affecting the intent. The RAW_DC and LOW_VOLTAGE labels designated in FIG. 5 are instantiated in FIG. 6. RAW_DC is present at the juncture of C1 and F1, LOW_VOLTAGE is present at the juncture of U2 and C4. F1 disconnects the circuitry if a component failure occurs.

Voltage regulators (U2, D4) are linear buck regulators. A switching regulator may also be used. D2 may be a steering diode, or built of biased transistors, biased field effect transistors (FET), metal oxide field effect transistors (MOSFET), transistors, and thyristors.

Capacitors (C1-C5) are commonly available types well known to one skilled in the art. They include tantalum, ceramic, and aluminum electrolytic types.

The CONTROL (FIG. 5, block 20) is comprised of U1, P1, JP1, R1, R2, R4, and D5 in FIG. 6. P1 is present so that U1 can be programmed after the unit is assembled. JP1, R1, and R4 allow the NoIce Control to be calibrated. R2 and D5 are present to present a visual indication that the unit is operating properly. JP1, P1, R2, and D5 are not necessary for proper unit operation, they are provided as a convenience for manufacturing and quality control.

This embodiment of the NoIce Control uses a microcomputer from Cypress Semiconductor (CY8C21123) for U1 to monitor the temperature of the evaporator coil. Other similar microcomputers are available from Silicon Laboratories, Intel, On Semiconductor, Texas Instruments, Microchip Technology, Fairchild Semiconductor, and ST Microelectronics, among others. The microcontroller has a built-in signal converter with which to read the raw NTC voltage value, and enough memory and mathematical operators to allow it to convert that reading to an accurate temperature. The microcontroller also has the necessary processing capability to maintain an operations list (such as time-versus-temperature, run time, and other parameters), and decision-making instructions, to allow it to determine whether an operational fault necessitating interrupting the CfC command signal has occurred.

The INTERFACE (FIG. 5, block 30) is comprised of D1, C2, and R3 in FIG. 6, and is designed to operate a Vishay NTC thermistor. R3 (Vishay MCT06030C1002FP500) is a single, precision resistor that scales the sensor output to U1. This connection arrangement converts the NTC thermistor's temperature-driven resistance change to a voltage that varies with temperature. C2 removes transient noise from the thermistor signal and D1 clamps external noise which may influence the readings or harm U1.

The DRIVER (FIG. 5, block 40) is comprised of R6, R7, Q1, Q2, and in FIG. 6. The driver activates the interrupter on command from the controller. Signal interruption is accomplished when U1 sets pin 0.2 low, which turns off Q2 (Fairchild MMBT3904). Q2 off then turns K1 (block 60) off, opening the CfC command signal, and simultaneously turns Q1 on, lighting D6 (LED), which alerts the user to the fault. The components R5, R6, and R7 are resistors used to limit currents through various parts of the circuitry, and their values were chosen using standard engineering practice.

The TEMPERATURE SENSOR (FIG. 5, block 50) used in the preferred embodiment is an inexpensive Vishay NTC thermistor, part number NTCLE100E3103HBO. The two leads from the device are interchangeable and connect to pin 1 and pin 2 of J1. Other types of temperature sensors are also available, such as silicon diodes from Fairchild Semiconductor (Sunnyvale, Calif.), RTD devices from Yellow Springs Instruments (YSI, Yellow Springs, Ohio), or digital temperature integrated chips (ICs) from Texas Instruments (TI, Dallas, Tex.). Each of those other devices has a different set of accuracy and precision capabilities, each has a different implementation cost, and each has a different electrical interface to the control.

The INTERRUPTER (FIG. 5, block 60) is comprised of K1, D3 and F2 in FIG. 6. The contacts of K1 disconnect the thermostat CfC line from the compressor, F2 protects the circuitry if a thermostat or compressor failure occurs, and D3 protects the circuitry from the inductive kickback of the K1.

The ALERT (FIG. 5, block 70) is comprised of R5 and D6 in FIG. 6. This embodiment uses a visual fault indicator; other embodiments may instead, or also, use audible alerts or other types of system connections to alert the user.

The preferred embodiment of the NoIce Control is designed to be installed by relatively unskilled workers, using only wire colors as the indicators for proper connection. Unlike more invasive installations, this unit requires only three wires to install. From FIG. 5, the CfC command (Wire 12, yellow) may be connected to the NoIce Control on P2, either pin 1 or pin 3. The signal then exits the NoIce Control for the refrigerant compressor (wire 14, also yellow) on the other pin. The wires are colored yellow to match the standard color used for control wires in the HVAC industry, and this minimizes the training requirements for the installers. The third wire, the thermostat common connection, is connected to P2 pin 2 and is colored blue to match the color used in the industry for thermostat common. The interruption of the CfC command signal is the critical connection of this device into the system. As stated above, the typical control connects a CfC command signal from the thermostat to the refrigerant compressor to effect system operation. In earlier systems, interruption of this signal was handled using a mechanical contact, either a mercury switch or a relay. Using modern electronic devices, signal interruption may be carried out using a Triode AC switch (TRIAC) or a silicon controlled rectifier (SCR) (from Fairchild Semiconductor or Diodes, Inc. for instance), or may be handled using relay contacts (from Potter-Brumfield, Panasonic, or Omron, for instance).

The operational parameters of the unit (times and temperatures in FIG. 7) were determined empirically, and are included here for reference only. Other parameters and other manufacturers' components may be used in this implementation without affecting the intent.

The conception upon which this disclosure is based may be utilized readily as a basis for designing other structures, methods and systems for carrying out the several purposes of the present invention by those skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. The claims must be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 

We claim:
 1. A reversibly wireable evaporator freeze-over prevention device comprising, in combination: a. a rectifier and regulator which may use either of two like color coded wires as an input, the second like color coded wire as an output and a third wire as common; b. a driver electronically coupled to an interrupter wherein the interrupter may open the connection between the input and output; c. a controller which may time events and measure a sensor signal, which controller is electronically coupled to the driver, to an alert device, and to an interface an interface electronically coupled to a temperature sensor.
 2. A reversibly wireable evaporator freeze-over prevention device as recited in claim 1 wherein the alert device is a visible alert.
 3. A reversibly wireable evaporator freeze-over prevention device as recited in claim 1 wherein the alert device is an audible alert.
 4. A reversibly wireable evaporator freeze-over prevention device as recited in claim 1 wherein the alert device is a connection to a network in which to send an alert message.
 5. A reversibly wireable evaporator freeze-over prevention device as recited in claim 4 wherein the connection to a network in which to send an alert message is a wireless connection. 